This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Many Gram-negative pathogenic bacteria employ a sophisticated protein secretion apparatus termed type III secretion system (T3SS) to transport bacterial effector proteins into eukaryotic host cytoplasm. The translocon, a structural component of T3SS, is a protein complex that traverses the host cell membrane for translocation of effector proteins. The molecular mechanisms underlying the T3SS protein translocation remain unclear. Our research is focused on the structures of Shigella translocon proteins IpaB and IpaC and their chaperone IpgC. IpgC single crystals have been obtained and optimization is underway. Histidine kinases have been attractive new targets for drug design to circumvent drug resistance in Grampositive pathogenic bacteria. Our research is aimed at structure and function of a multidomainal, membrane spanning histidine kinase from an essential two-component signal transduction system.